Invasion percolation model for abnormal time-dependent dielectric breakdown characteristic of low-k dielectrics due to massive metallic diffusion

With the continuing aggressive scaling of interconnect dimensions and introduction of lower k materials, back-end-of-line (BEOL) dielectric time-dependent dielectric breakdown (TDDB) reliability margin is greatly reduced. In this paper, a comprehensive investigation on abnormal low-k TDDB characteristics, a systematic degradation of Weibull slopes, and a systematic increase of field acceleration at lower stress voltages due to massive Cu diffusion were conducted for Cu interconnect with low-k dielectric. Based on data from extensive electrical and physical analysis, such abnormal TDDB characteristics were attributed to slow metallic diffusion in bulk low-k under bias and temperature stress. A TDDB model based on invasion percolation was proposed to model the observed abnormalities. Cu interconnects with robust liner and capping layer, to ensure metal free low-k film, have become important for BEOL low-k TDDB.